The present invention relates to a method for determining reference points in a fingerprint.
A method for generating a digital gray-scale image of a fingerprint for analyzing the minute details is discussed in U.S. Pat. No. 5,926,555. The minute details are determined using a signal-matched filter. Also, reference points such as core points or delta points are determined here. The digital gray-scale image is transformed into the frequency range, and is rid of distortions using a lowpass filter, a contrast-enhancing filter, or a bandpass filter. The fingerprint is analyzed in image areas of the gray-scale image.
It is believed that an exemplary method for determining reference points in a fingerprint according to the present invention may have the advantage of attaining increased reliability in determining reference points, i.e., singularities, in fingerprints. In this way, it is believed that there is significantly greater reproducibility in determining the reference points and in the fingerprint analysis as such.
Additionally, it is believed that the exemplary method and/or exemplary embodiment according to the present invention provides for placement of the fingers on the fingerprint sensor to be unimportant for analysis of singularities, as long as these singularities are still on the fingerprint image. This is achieved by determining a global orientation of finger pressure after determination of the singularities. In this way, determination can be made in what direction the finger is placed on the fingerprint sensor. This is achieved by determining the position of identified reference points with respect to each other. Additionally, the exemplary method and/or exemplary embodiment according to the present invention provides for concluding that a singularity exists on the finger, even if this singularity is not contained in the fingerprint because the finger was not entirely placed on the fingerprint sensor.
It is believed that another advantage is that the exemplary method and/or exemplary embodiment according to the present invention may achieve a better analysis of the dermal ridge patterns. An exact point analysis is done which results in no fusion of assessed values for orientation. Thus, the spatial resolution of the exemplary method and/or exemplary embodiment according to the present invention may be increased.
It is also believed that xe2x80x9cprecisexe2x80x9d continuous orientation assessment provides for an unambiguous determination of reference points (spatial resolution), which may also be advantageous in regard to placement of the finger on the fingerprint sensor. But in this regard, it is believed to be at least important that a two-dimensional comparison be made of orientation values with stored reference orientation patterns.
Because image distortions are eliminated, it is believed that the exemplary method and/or exemplary embodiment according to the present invention may be particularly robust vis-a-vis such distortions. It is believed that using the exemplary method and/or exemplary embodiment according to the present invention provides for identifying the arch type as a reference point, which has no singularity per se. Determination of reference points makes it possible to fix global coordinate systems, independent of minute details, for description of local features. This should considerably facilitate or at least facilitate identification of a fingerprint, and thus of a person. Also, for correlation of stored fingerprints with new fingerprints, unambiguous determination of the areas to be correlated via the exemplary method and/or exemplary embodiment according to the present invention is believed to be provided, so that correlation is also improved. A global rotation angle is believed to provide for correlation of fingerprints rotated with respect to each other.
Also, via similarity values which are computed in comparing the orientation patterns with reference orientation patterns, it may be assessed whether a reference point is found or not. In this regard, its xe2x80x9cvery precisexe2x80x9d position may be identifiable in particular.
Furthermore, via determination of reference points, whorl, delta and core points are identifiable. These are points that occur in a fingerprint as singularities.
Furthermore, in determining core points, a two-step process is used, with a linear reference orientation pattern in the first one and with a nonlinear reference orientation pattern in the second one. Thus, greater precision may be achieved.
For computing similarity values, the determined orientation patterns may be converted into a vector field, which should simplify determination of similarity values.
Determining the scattering of spectral power density in the usable frequency range provides for xe2x80x9cstatingxe2x80x9d a coherence value, which allows image areas severely impaired by distortions to be eliminated from the analysis. This should increase the reliability of the exemplary method and/or exemplary embodiment according to the present invention, and thus the reproducibility of the analysis to be carried out.
Furthermore, the limit frequencies of the bandpass may be pre-set by the minimum and maximum dermal ridge interval, so that no usable data is filtered out of the image area.
Finally, an exemplary device is provided for determining reference points to carry out the exemplary method according to the present invention. This is, for example, a fingerprint sensor with an attached computer that carries out the analysis.